Electrically charged objects, such as, for example, electrical medical equipment, may generate electromagnetic (EM) fields. EM fields may affect the behavior of other charged objects in the vicinity. Mathematical relationships, such as Maxwell's and Faraday's equations and the Lorentz force law, demonstrate that radiated EM fields can induce electric currents on nearby equipment. These induced currents are generally referred to as electromagnetic interference (EMI), and they may interfere with or corrupt electrical signals generated by nearby medical equipment. In a medical setting, such as an operating room or a physician's office, electrical equipment may generate EM fields that affect other medical instrumentation in the vicinity. While medical equipment may be regulated and tested according to industry standards in order to limit the magnitude of EM fields produced, EM fields and radiation may also be generated by other equipment present in a medical facility.
In the case of a digital endoscope, electrical equipment, such as imaging systems, including cameras located on a distal region for viewing an internal region, may be affected by such EM fields. The EM fields generated by surrounding equipment may couple with cables associated with a digital endoscopic camera, corrupting signals relayed to and from the camera. EM fields may also couple with electronic cables connecting distal endoscopic components, like the digital camera, to proximal electronics, for example, an imaging processor. Additionally, any other electrical components placed near the EM source may be corrupted.
This corruption from stray current, sometimes referred to as “airborne EMI,” may have a detrimental effect on endoscopic medical equipment. Cables connecting the distal and proximal electronics of an endoscope may be particularly susceptible to corruption, because the conductors within the cables may act as long antennae, attracting electrical noise from the EM field. These cables may transmit video signal from a distally located endoscopic camera to proximal video processing equipment. In the case of endoscopic imaging equipment, the coupled EMI may corrupt video signal, causing image degradation or, in some instances, complete loss of video imaging. Thus, there exists a need to reduce EM field noise coupling to endoscopic cabling.
One method of reducing the effects of coupling from airborne EMI to endoscopic cables involves twisting the individual cable conductors together. Twisting the conductors may uniformly expose each conductor to substantially the same noise. Electronic hardware and/or software may then be able to detect the similar signal components, i.e. noise, across each individual cable conductor, allowing the hardware and software to subtract that noise uniformly from the total signal output. However, twisting conductors or conductor pairs may not always be feasible. For example, some medical devices, such as endoscopes, may have size constraints to allow them to navigate narrow body lumens. Because twisting conductors may add additional bulk to the cables, this method of noise reduction may not be possible for some devices.
Another noise-reduction technique includes surrounding noise-sensitive cables with an EMI shield. Such shields may include, e.g., copper tape or EMI shielding paint, which may be painted on the cabling enclosure, for example. Adding EMI shielding may increase the cost of such devices, however, which is a concern particularly for disposable endoscopes. In some cases, the addition of an EMI shield may be difficult or impossible. For example, it may not be possible to coat the internal lumen of a catheter with EMI shielding paint.
Noise coupling may also occur through a conductive medium, for example, saline or bodily fluid. This source of noise coupling may be referred to as “conductively coupled noise.” For example, if an electrical signal is applied to a volume of saline solution, a resulting signal can be measured on an electrode placed in contact with the saline. The saline acts as a conductive path, allowing the injected signal to couple with the electrode. For a medical device, such as an endoscope, bodily fluid or saline used for irrigation, for example, may surround portions of the internal electronic cabling when the endoscope is exposed to such fluidic environments. The conductivity of this fluid medium thus increases the potential for noise coupling between the fluid and the cables.
One method of decreasing conductively coupled noise is to reduce the amount of fluid in contact with the cabling. Placing the cabling in a separate, sealed lumen may prevent fluids from contacting the cabling. Yet, the size constraints of endoscopes may make sealing the cables difficult. For example, a wall between a visualization lumen of an endoscope and an irrigation and/or aspiration lumen may be thin, for example, to reduce size or increase flexibility. Consequently, the thin wall may be prone to processing defects and/or mechanical damage during a medical procedure. These defects may allow fluid from the irrigation and/or aspiration lumen to enter into the visualization lumen. When an electronic imaging endoscope is used, fluid may surround an electrical cable disposed in the visualization lumen and may fill available space between adjacent conductors of the electronic cable assembly. This may result in imaging signal degradation or failure. Additionally, manufacturing thin walls capable of increased fluid impermeability may also increase the cost of medical devices.
Another method of reducing conductively coupled noise is to electrically insulate the signal conductors using insulation around the cable. However, the insulation must be of sufficient thickness to prevent noise from coupling to the internal conductors. As a result, using insulation may add to the space requirements of a medical device and therefore may not be feasible for use in smaller-diameter devices, such as endoscopes. Accordingly, a need exists for a means of insulating cables from environmental noise and/or fluid without increasing space requirements, decreasing flexibility, or increasing the cost of a digital imaging endoscope.